In renal failure patients, poor kidney function results in the accumulation of waste products and excess water in the blood. Hemodialysis uses an “artificial kidney” to remove these waste products and excess water from a patient's blood. In this procedure, the patient's blood is flowed over one side of a semi-permeable membrane while a dialysate is flowed in an opposite direction on the other side of the membrane. Osmotic pressure causes the waste products and excess water to selectively flow across the membrane into the dialysate to reduce their concentration in the patient's blood.
Over the last several decades numerous technological improvements have made this procedure safer and more effective. Nonetheless, because a large amount of blood must be transferred between a patient and a dialysis machine, it remains subject to complications such as infection and bleeding. It is also inconvenient to patients as it requires about 2-4 visits to a dialysis center each week.
To reduce complications and inconvenience, a number of methods and devices have been developed which facilitate repeated access to a patient's blood. These include intravenous catheters, synthetic grafts, and AV fistulas. Most dialysis patients receive dialysis using AV fistulas or AV grafts (made of heterologous material such as plastic, PTFE, or animal arteries). Because both fistulas and grafts must heal or mature prior to use, when most patients in urgent need of dialysis first present at a clinic, access to the bloodstream is obtained by tunneling silicone catheters through the superior vena cava via a small incision in the neck into an area adjacent to the right atrium of the heart. The end of the catheter opposite the atrium is then tunneled through the chest tissue to an exit site in the skin where it can be accessed.
While effective, tunneled catheters are also subject to serious complications. The main problem with placing the tunneled catheters in the heart is that the catheter itself can cause scarring of veins leading to stenosis (central vein stenosis)—particularly in patients having multiple catheter placements over many years and in those who develop catheter infections. Patients with catheter-related central vein stenosis are often unable to utilize fistulas or grafts because the stenosis impedes the flow of blood back from the fistulas or grafts and causes severe swelling of the limb where the fistula or graft was created. Long-term use of tunneled catheters almost always causes infection at the catheter placement site so is not practical. Accordingly, many patients with catheter-related central vein stenosis die because surgeons can no longer create a long-term access site.